Beat the beetles: NAU researchers crank up the volume to fight tree-killing pests

Entomology professor Richard Hofstetter is studying infested ponderosa pine trees. Under the bark, bark beetles tunnel, mate, lay eggs and eat the living part of the tree. Photos courtesy of Ecological Restoration Institute

A phenomenon dubbed “Beetle Mania” is playing out in northern Arizona. As can be expected, it involves rock music, but instead of screaming fans there are cheering scientists who have found a way to drive bark beetles crazy with sound.

In a Northern Arizona University School of Forestry lab, researchers are listening to the sound of Western forests under attack: the scratching, scraping, crunching of the Ips bark beetle and its cousins chewing the life out of ponderosa, pinyon and lodgepole pines.

Armed with sonic bullets, they are firing back with Rush Limbaugh, Queen, Guns N’ Roses and manipulated sounds of the bugs themselves.

“Our interest is to use acoustic sounds that make beetles uncomfortable and not want to be in that environment,” said NAU professor Richard Hofstetter.

Barely a quarter-of-an-inch long, bark beetles are tiny and powerful killers. When they amass by the thousands, they become a lethal army, tunneling through millions of acres of trees already stressed by drought and overcrowded forest conditions.

The Ips bark beetle, shown here in a Petri dish, is barely a quarter-of-an-inch long, but this tiny killer can destroy millions of acres of trees when attacking by the thousands.

“You can get thousands, even tens of thousands of bark beetles colonizing a tree and that tree can die very quickly, within a day or two,” Hofstetter said.

The evidence for this exists all over the West. In fact, the beetles’ British Columbia invasion that ended last year wiped out some 10 million acres.

Pondering this deadly infestation is truck-driver-turned-research assistant Reagan McGuire. “I read an article in the local paper that bark beetles have killed 74 million trees in Arizona and New Mexico. So I got to thinking, what if we could fight back with sound, what if we could alter their behavior by producing acoustic stress.”

After McGuire persuaded Hofstetter to look into this kind of research, he quit his truck driving job and joined the lab.

“I thought, ‘What would be the nastiest, most offensive sound?’ To me, that would be Rush Limbaugh or heavy metal,” McGuire said.

Researchers began collecting infested tree trunks in the fall. Because bark beetles live and tunnel through the phloem—a tree’s living tissue just under the bark—they started creating phloem sandwiches, slices of infested pine trees encased in Plexiglas, to build ant farms of sorts. Using tiny speakers like the kind in musical greeting cards, researchers piped sound in and also recorded sounds coming out, sounds the bugs were making.

They blasted the beetles with rock music and Limbaugh commentary played backward. Discouraged by the results, the scientists started firing the insects’ own sounds back at them. They couldn’t believe what they saw.

School of Forestry research assistant Reagan McGuire listening to agitated bark beetles when they hear manipulated sounds of themselves.

“We could use a particular aggression call that would make the beetles move away from the sound as if they were avoiding another beetle. Or we could make our beetle sounds louder and stronger than that of a male beetle calling to a female, which would make the female beetle reject the male and go toward our speaker,” Hofstetter said. “We found we could disrupt mating, tunneling and reproduction. We could even make the beetles turn on each other, which normally they would not do.”

Wearing a headset, McGuire would listen and watch the beetles on a computer monitor hooked up to a microscope. “We observed and recorded beetles mating two or three times. Then we’d play the beetle sounds that we manipulated and watch in horror as the male beetle would tear the female apart. This is not normal behavior in the natural world.”

So in the spotlight and under the microscope are bark beetles and their communication sounds and patterns.

Researchers are seeking funding to help them continue looking for the sound—perhaps ultrasound—that can be used strategically to keep beetles from damaging individual or entire stands of trees.

Right now, bark beetles are hibernating in the snow-covered forests, where they will awake to a feast of vulnerable trees. But inside the lab, scientists are waiting to greet the sleepy pests with what they hope will be a rude awakening.

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